If the previous company is not providing you with a relieving letter, you may proceed to join another company by issuing a 2-month notice to your previous employer. It is important to mention in the notice that the previous company has not provided the relieving letter, as this information will be useful for future correspondence. It is the responsibility of the employer to furnish a relieving letter with due diligence, ensuring it is provided within 2 months from the date of resignation.